Research Journal of Agriculture and Biological Sciences, 3(5): 367-369, 2007

© 2007, INSInet Publication

Iodimetric Determination of Ascorbic Acid (Vitamin C) in Citrus Fruits

1
Department of Chemistry, Adeyemi College of Education, Ondo, Nigeria.
2
Department of Home Economics, Adeyemi College of Education, Ondo, Nigeria.

Abstract: The ascorbic acid content of the juices of four different citrus fruits – orange, tangerine,
grapefruit and lime was determined iodimetrically in order to know which fruit would best supply the
ascorbic acid need for the body. Results showed that orange had the highest value of ascorbic acid, 600
µg /mL followed by grape, 446 µg /mL and then tangerine, 415 µg /mL. Lime had the least value, 306
µg /mL. It therefore follows that orange would supply more ascorbic acid per milliliter for body need
compared to the other three fruits. In fact, the value of ascorbic acid in orange is about twice that of lime.

Key words:

INTRODUCTION body stores of vitamin C fell bellow 300 mg, and their
gums and skin lost the protective effects of vitamin C.
Long before the discovery of vitamin C (ascorbic Vitamin C is reported to lower cancer risk,
acid) in 1932, nutrition experts recognized that regenerate vitamin E sup plies, imp rove iron
something in citrus fruits could prevent scurvy, a absorption [6 ] and high-dose of it protects the eye against
disease that killed as many as 2 million sailors between cataracts [7 ]. Vitamin C is said to have important
1500 and 1800 [1 ]. interactions with other vitamins. For example, excessive
The use of lime for the prevention of spoilage of intake of vitamin A is less toxic to the body when
palm oil on storage had for long been in practice vitamin C is readily available [6 ].
among the traditional farmers, especially in the western Various reports show that fruits are excellent
part of Nigeria. W ithout any formal education they sources of vitamin C. Citrus fruits, tomatoes,
knew that lime contained something that would not strawberries, bell peppers and broccoli are good
allow the oil to go rancid. The practice was to press examples of food fruits rich in vitamin C [5 ]. The reports
the sliced lime to release its juice on the spongy cover of the vitamin C content of natural food-fruits include
used for sealing the tin containing the palm oil for the citrus fruits. A serving size ¾ cup of orange juice
storage. By so doing, the farmers could preserve their from frozen concentrate is reported to contain 75 mg
oil for several months without getting spoilt. W ith the of vitamin C; one medium size orange, 60 mg; half a
discovery of vitamin C, it is now known that the white grapefruit, 40 mg; and one medium size
antioxidant in the lime that prevented the oil spoilage tangerine, 25 mg of vitamin C [3 ]. Limejuice is reported
is vitamin C or ascorbic acid. to contain 29 mg of vitamin C per 100 g juice [8 ].
Vitamin C is a white crystalline compound highly Nutritionists generally regard any ‘serving’ of food
soluble in water. It is not a carboxylic acid but a that provides 10% to 25% of the daily vitamin C need
lactone, and owes its acidic properties and ease of in a relatively low calorie package as a ‘good’
oxidation to the presence of an enediol grouping [2 ]. The source [8 ]. The 1989 recommended daily allowance
vitamin plays a role in controlling infections and the (RDA) for an adult is 60 mg per day (this is based on
body’s response to stress. It is also found to be a the amount of vitamin C needed to prevent clinical
powerful antioxidant that can neutralize harmful free scurvy and provide body stores sufficient to prevent
radicals; helps make collagen, a tissue needed for scurvy for around 30 days plus “a margin of safety”).
healthy bones, teeth, gums and blood vessels [3 ,4 ,5 ]. As At April 1999 it was being officially recommended,
early as the 1700’s, vitamin C was referred to as the based on new information that the RDA ought to be
“antiscorbutic factor”, since it helped prevent the changed to 120 mg per day [9 ].
disease called scurvy. This disease was first discovered In the United States, the current (2000)
in British sailors, whose sea voyages left them far from recommended daily allowance (RDA) or Adequate
natural surroundings for long periods of time. Their Intake (AI) for vitamin C is 90 mg per day for men

Corresponding author: A.A. Izuagie, Department of Chemistry, Adeyemi College of Education, Ondo, Nigeria.
E-mail: anthonyizuagie@yahoo.co.uk

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 Res. J. Agric. & Biol. Sci., 3(5): 367-369, 2007

and 75 mg per day for women. The given AI value for study. Some of the fruits were peeled and cut into two
men is for males 19 years and older, while that for transversely and then squeezed to discharge their juice
women is for females 19 years and older. It is into a pre-washed beaker. Sufficient juice was obtained
recommended that smokers consume 35 more for each kind of citrus fruit used for the experiment.
milligrammes of vitamin C per day. Pregnant and The seeds were carefully picked out from the juice. A
lactating women have AI values as high as 85 and 120 25 mL aliquot of each juice was titrated against the
mg respectively for 19 years or older [1 0 ]. In the standard 5.6076 x 10 -3 M iodine solution to a light blue
April 10, 2000 press release, National Academy of end point using freshly prepared starch as indicator.
Sciences (NAS) set a Tolerable Upper Intake Level
(UL) for vitamin C at 2000 mg (2 g) for adults 19 RESULTS AND DISCUSSIONS
years or older [9 ].
Recent surveys of the U.S. Department of The average titre of iodine in three determinations
Agriculture (USDA) show that the average intake of having corrected for blanks are reported in Table 1.
vitamin C by American adults was over the AI Iodine is produced in the reaction according to the
for vitamin C. W omen tended to consume less following equation:
than men of the same age [1 1 ]. Taking too much
vitamin C is reported to cause side effects such as IO 3 - + 5I - + 6H + 3I 2 + 3H 2 O (1)
nausea and diarrhea [5 ].
Vitamin C is lost from foods during preparation, IO 3 - + 8I - + 6H + 3I 3 - + 3H 2 O (2)
cooking, or storage. Therefore to prevent loss Triiodide
of vitamin C, the following precautions are ion
recommended [3 ]:
Equation (2) is as a result of excess K I that keeps
C Serve fruits and vegetables raw whenever possible; the iodine in solution as a triiodide ion.
C Steam, boil, or simmer foods in a very small The equation for the quantitative reaction of the
amount of water, or microwave them for the triiodide ion and the vitamin C (ascorbic acid) is
shortest time possible;
C Cook potatoes in their skins. Be sure to wash the
dirt off the outside of the potato;
C Refrigerate prepared juices and store them for no
more than two to three days;
C Store cut, raw fruits and vegetables in an From equation (2), it is seen that vitamin C and
airtight container and refrigerate- do not soak or the Triiodide ion react in ratio 1:1. it is therefore easy
store in water. to calculate the molar concentration of the vitamin C
in each juice as expressed in Table 1.
The objective of the study was to determine the Since the molar mass of vitamin C is known
vitamin C content of the citrus fruits with the view of (molar mass = 176.123 g/mol), and the volume of juice
making recommendations for their intake. used in each determination was 25 mL, then,

M ATERIALS AND M ETHODS Table 1: Average titre of iodine solution in titration of iodine
against vitam in C in citrus Juices
Fruit Average titre of M olar concentration of
A standard iodine solution was prepared by
three determ inations (m L) vitam in C in the juice
dissolving 0.2g of KIO 3 and 1.6g of KI in some
distilled water in a 500 mL volumetric flask. The KI O range 15.20 3.4094 x 10 -3
was well in excess to keep the I 2 generated in solution Grapefruit 11.30 2.3552 x 10 -3
as I 3 -. The solution was acidified by adding 1 mL of Tangerine 10.50 2.5346 x 10 -3
Lim e 7.75 1.7384 x 10 -3
concentrated tetraoxosulphate (VI) acid (H 2 SO 4 ). The
mixture was swirled and the volume of solution raised Table 2: V arious expressions of concentrations of vitam in C in
to 500 mL with distilled water. The flask was citrus fruits
stoppered and shaken to ensure homogeneity of Citrus fruit juice Concentration of vitam in C in juice in
-----------------------------------------------------------
content. Thus, the concentration of iodine solution was
µg/m L m g/L m g/10cL
5.6076 x 10 -3 M. The iodine solution was kept in a O range 600 600 60.0
closed cupboard. Tangerine 415 415 41.5
Some fresh ripe oranges, grapefruits, tangerine and Grapefruit 446 446 44.6
lime were obtained from their respective trees for the Lim e 306 306 30.6

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its concentration could be expressed in µg/mL, mg/L or 3. Ohio State University, Department of Human
mg/10cL as shown in Table 2. Nutrition and OSU Extension 2004. Vitamin C
To meet the 90 mg recommended daily allowance (Ascorbic Acid)., HYG-5552-05.
(RDA) for vitamin C [1 0 ], as much as 15 cL or 150 ml 4. Carr, A.C. and B. Frei, 1999. Toward a new
of orange juice will have to be taken. A medium size recommended dietary allowance for Vitamin C
orange, 216.7g yielded 76mL juice. This implies that based on antioxidant and health effects in humans.
taking two oranges of that size daily would ensure Am. J. Clin. Nutr., 69: 1086-1107.
adequate of vitamin C. Drinking 25 cL of either 5. Hwang, M.Y., 1999. How much vitamin C do you
grapefruit or tangerine juice would supply 90 mg of need? The Journal of the American Medical
vitamin C required for daily need. However, about 30 Association., 281(15): 1640.
mL of lime will have to be taken to meet the same 6. Mateljan, G., 2007. The world’s healthiest foods:
daily requirement of vitamin C. Vitamin C. whfoods.org.
7. Sardi, B., 2000. Is high-dose vitamin C risky?
Conclusion: Of the citrus fruits only orange and 8. N a tur a l fo o d -fru it v ita m in C content.
tangerine have a sweet taste and are more convenient http://www.naturalhub.com/natural_food_guide_fru
to swallow. The juices of grapefruit and lime are it_vitamin_C.htm.
somewhat bitter and sour to taste respectively. To meet 9. Levine, M., S.C. Rumsey, R. Daruwala, J.B Park
the RDA of 90 mg, their juices may be more and Y. W ang, 1999. Criteria and recommendations
conveniently taken at different times in portions. for vitamin C intake. The Journal of the American
The juices of oranges and tangerine are hereby Medical Association., 281(15): 1415-1423.
recommended, preferably, to be taken daily during meal 10. National Academy of Sciences. Press release,
at quantities sufficient to meet daily vitamin C need. April 10, 2000.
Taking vitamin C especially during meal will assist in 11. U.S. Department of Agriculture, U.S. Department
reducing iron III to iron II, which is of benefit to the of Health and Human Services. Your Health:
body. Dietary Guidelines for Americans, 4 th ed. Home
and Garden Bulletin No. 232. U. S. Government
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